Single vs Twin

[Flyboy-F33]

I'm sure this may have been discussed before but....

I would be interested in hearing peoples views on the perceived benefits of twin engined operations over a high performance single, lets say a Baron 55 or 58 / Cessna T310R v's a Bonanza or Mooney 252.

Very little difference in initial purchase price between them all right now due to the dollars position, so what factors would make you choose one over the other?

GG:ok:

[cblinton@blueyonder.]

Well Flyboy, its a difficult one! it all depends on what budget you have really.
You also have the safety factor over water and in IMC.
When you look at performance there isnt much in it, my Bonanza will see off some twins in the cruise with far less fuel consumption and less maintenance so really it depends on ya wallet.

Best of luck with your decision:ok:

[FlyingForFun]

Summary of what I've read on other threads:

- Single: Cheaper to run. Obvious safety issues over large bodies of water, in or above low-level cloud, and at night.

- Twin: Expensive to run, but none of the safety concerns of singles as long as the pilot is current. However, a pilot who is not current is arguably more dangerous than the dangers of the single.

FFF
--------------

[Oscar Duece]

Try best of both worlds. A Cessna 337:ok:

[Flyboy-F33]

337....no thanks, far too noisy.

To clarify the situation, I already have a Bonanza, but am trying to decide wheter or not to move up to a twin. Do the benefits outweigh the extra fuel costs and maintenance on the second engine? Is there a real speed benefit? Is there anything else I have overlooked?

GG:}

[OFBSLF]

What's the performance of the twin on a single engine? I was under the impression that single engine performance of some light twins is poor enough to be rather exciting.

[bluskis]

It comes down to one word, safety. If safety is not your number one priority you may not wish to incurr the extra cost. It does appear from what you say you can afford to make the transition, and as to the marginality of some twins, the answer is don't buy a marginal model.

With the requirement for annual verification of piloting skills the old arguements about EFOT dangers are old hat.

[IO540]

Why not a turboprop single? According to some NTSB data I read a while ago, one of these is five times less likely to come down than a piston single.

Here's a good one:

http://www.grob-aerospace.de/get.php4?pageid=133

Does cost a bit more than your average 30 year old twin though :O

[bluskis]

Some problems with handling on approach with some turboprop singles, see recent threads

Some thirty year old twins are better than some later twins. It is important to research the performance of the various models before buying.

[IO540]

bluskis

Some problems with handling on approach with some turboprop singles

Only because some have lots of power relative to the aileron authority at low approach speeds. But... can you ever have too much power? I would rather have 400bhp and remember to use the rudder, than have 200bhp.

[Flyboy-F33]

Okay, so how do we define a 'marginal' twin? Is it based on single engine ceiling or single engine rate of climb? How much is marginal, how much is acceptable?

GG

[bookworm]

I like FFF's summary. Only thing I would add is field length.

The place the twin bites harder than the single is from about 60 knots on the t/o roll to the point at which you're climbing comfortably away well above blue line speed. Between those two points, you have some tough choices to make if you suspect an engine problem (note not "have an engine failure") in a twin. A long runway makes it easy -- close the throttles and land straight ahead if you're airborne. On a short runway, doing so becomes a hull write off.

So even if the twin's performance is well within the field declared distances, you may prefer a single where the decision making is easier.

J Mac McClellan of Flying (http://www.flyingmag.com/) went through a Bonanza to Baron upgrade many years ago. Why not email him for advice?

[E1453]

Having seen the latest ultralights and the Cirrus, I'm inclined to think that piston twins will become redundant soon.

Those new planes I mentioned are equiped with BRS, a balistic chute with a rocket, wich can be deployed quickly and bring you and the airplane safely to the earth.

Except for the takeoff and initial climb, the chute should work properly and make a second engine redundant.

Well, as in many twins, with a high useful load, the safest procedure with one engine out may be to abort and crash ahead anyway (a forced landing is better than a spin dive), the safety advantage of the twins over singles are MUCH smaller if the single has a BRS.

I think that the "danger window", in a single with a BRS, would be too close to the window of a light twin, so the extra costs would not be necessary.

[Timothy]

On the occasions when this question is asked (and it is asked often) I am often tempted to roll out again an article I wrote for the PPL/IR network as to why I took the decision. Apologies to those who have read it before.


Until about ten years ago I operated a Cessna 172 Skyhawk as my business aircraft. It was airways equipped, I was instrument rated (indeed had an ATPL/IR and had been employed as an executive jet captain in the recent past) and there should have been little except (relatively rare) 500m RVRs to prevent me from flying on business all over the country.

But I didn't. Almost every time a meeting or trip came up which obviously demanded aviation I found myself deciding that using the 172 was not appropriate. The reasons that the flight might not be possible multiplied in my mind...icing, low cloud, thunderstorms, long water crossings, night flights, electrical and avionics failures, strong headwinds en-route, strong crosswinds on arrival...the list seemed endless.

I was not cancelling flights on the day because of these reasons. Rather, I was making alternative plans because I feared that the trip would have to be cancelled at the last minute, thus jeopardising my business.

There were two seminal moments in my decision to dump the 172.

The first was when I was sitting on the threshold at Fairoaks and the thought occurred to me:

"Here I am with one engine, one alternator, one vacuum pump, one pitot/static source and one pilot. If I were in the jet and any one of these situations arose I would declare an emergency and land...yet here am I about to take-off."

The second was when I had to go to an important meeting with the Blackpool Pleasure Beach, which is in walking distance of Blackpool Airport, a highly equipped, multi-runway, IFR, GA friendly airfield. Yet I still decided to drive from home, past the hangar where the 172 sat and then a further four hours, "just in case" there was a problem.

As I drove up the motorway and thought of the 172 sitting in the hangar, costing me a fortune in insurance, hangarage and maintenance I took the decision...either I get an aeroplane that has a reasonable expectation of delivering me or I give up on business aviation.

So, why was the 172 not reliable enough to be trusted to deliver me? There were a number of reasons, some demonstrable, others based on preference and prejudice.

The demonstrable reasons were icing, crosswind capability and speed.

Icing

I have never been one to get over-concerned about icing, and have from time to time carried a fair amount of ice on a non de-iced aircraft. Indeed I might go flying on a day when light icing is present in a height band. But the problem is that if icing is going to be present from the MSA up to FL100 you really cannot even think of getting the SEP out of the hangar.

Crosswind

Fewer and fewer airfields are offering a cross runway. A crosswind capability of 15kts means that the number of days which are outside limits at one end of the flight or the other reach significant levels.

Speed

Although at first glance going fast seems to be a luxury rather than a necessity, it becomes very relevant indeed when faced with a strong headwind. 50kt winds are not unusual at airway levels. This is nearly half the TAS of the single, leaving me with 70kts made good, whereas in a twin the groundspeed would be 120kts or better...nearly double the speed.

The factors based on preference or prejudice were all to do with system failures.

Engine Failure

I have had nine engine failures in my flying career. I know that they happen. This is why I always want a plan B available to cover the eventuality. Plan B in a twin is to divert at leisure. Plan B in a single should be to make a forced landing in a field. But that's rather difficult in hill fog, or even a 200' cloudbase, or at night, or over water, or over mountains. So if you fly a single and want to ensure that there is a plan B you are limited to flying over farmland, during the day, when the weather is reasonably good. So why bother with an instrument qualification?

Electrical or other systems failure

Almost as serious as an engine failure is an alternator failure in or above IMC. With no way of navigating or communicating you are left with some pretty unpleasant choices...flying triangles in the hope that someone will notice, then unrehearsed formation flying in cloud, or maybe dead reckoning to where you hope the sea is and then hoping that your guess at QNH is reasonably accurate. Similarly, loss of your single vacuum pump can be pretty fatal, particularly if you identify the symptoms late.

I know that there are counter arguments to some of the above. There are singles with redundant ancillaries, particularly alternators and suction pumps, there are de-iced and fast singles, and all of these make them more suitable for business flying than their lesser cousins. Nonetheless, they remain dependent on one power unit, and therefore everything continuing according to Plan A. Also, these highly equipped singles are relatively rare and expensive.

There are also some arguments against twins on safety grounds. The commonest are:

Risks associated with single engine failures on a twin

Most GA twins are not certified to be able to continue flying in the event of an engine failure below 200'. Twin training concentrates on failures above 200', recovery from such a failure and continuation of the flight. Unfortunately not enough emphasis is placed on the fact that below 200' the most prudent action is normally to shut down both engines and make a forced landing. The argument continues that if either engine fails, the result is a forced landing, and therefore the risk is at least doubled (I say at least because engines are marginally more likely to fail on a twin because of greater vibration and longer control runs.)

This increased risk is real and must be taken into account by the twin owner, but, at least in my mind, is more than offset by having the second engine available in the cruise, especially when conditions dictate that a forced landing is unlikely to be successful (water, mountains, night, low cloud etc).

Furthermore the time for which the aircraft is exposed to risk is very small (less than 15 seconds per flight) compared to the time spent exposed to risk in a single.

Finally, the pilot can do a great deal to mitigate the risk (using the full runway, rotating at blue line, avoiding built up areas in the take-off path etc). I have written an article in Flyer magazine on the subject.

Less protection in a forced landing in a twin

People do argue that in the event of a forced landing, uninjured survival of the passengers is less likely because the aircraft is going faster and the momentum is greater, the occupants are not protected by the engine going ahead of them and that the gear may be up and therefore not in a position to absorb impact.

I do not know if this is true, but even if it is, I consider it mitigated by the fact that a forced landing is much less likely.

Greater risks taken by twin pilots

There is an argument, developed, I believe, by Prof.Adams of London University, that no matter how safe a piece of equipment or transport is made, overall safety is not affected because the user will take greater risks until the risk level reaches the same point as it had been on the less safe equipment. Prof. Adams believes that Volvos should be replaced with paper cars with spikes in the middle of their steering wheels.

Thus, a twin is not safer than a single, because the pilot will choose to fly over water, in icing, at night, to IFR minima, where the prudent single pilot would not.

My counter argument is simply "...sure, maybe I am taking the same risk as a single pilot, but I am able to operate in much more difficult environments at the same risk."

Which means I can get to my business meetings. QED

[B2N2]

Well worded answer Timothy....
Even a Cirrus may not be safer due to pilot behaviour.
I have a healthy respect for multi engine flying and unless you stay current it's more dangerous than any single.
So the question is :
Do you need one?
Can you afford one?
Will you fly it enough to stay proficient?
I've recently advised somebody who was thinking about buying a multi to fly it at least 50hrs/year with a dual flight every month.
Less dual if you fly more than the 50 hrs but at least 2-3 dual flights a year even if you fly a lot!

[bluskis]

I would use single engine rate of climb following EFOTO to distinguish marginal from acceptable performance.

You can always make a command decision relative to the risks of single engine ceiling.

A twin that will reach single engine control speed before rotation on a reasonable length runway, say 2200/2400 ft would be one way of making the selection.

[IO540]

It seems to me that a turboprop with full TKS and a parachute would address all the reasons anybody would go for a light twin.

[englishal]

I would go for a twin with a CE ceiling of >10,000', which means turbo charging.

If you're going to do a substantial amount of flying, possibly IFR and crossing water, then the advantages of a twin will outweigh the disadvantages, though the costs will of course be 75% more than a single (Landing, parking, fuel fees etc). This may or may not be an issue to you. In a twin its still possible to complete an instrument approach on a single engine, in a SE there is no chance. A SE failure in the middle of the channel means you're going for a swim, in a twin it means you either a)aren't or b) have more time to get nearer to land before you go for a swim, and the helicopter can be waiting for you :D A SE EF over mountains, and its probably curtains for you, in a ME, you may have a second chance. A SE failure at night over desolate areas could prove very nasty, in a ME it may prove to be an inconvienience. In a twin, you're no worse off if you have an engine failure after take off than you are in a single if handled right, chances are you're going down, though maybe at a lesser rate than in a single (unless lightly loaded, flat terrain, aircraft type, you do everything right then you may climb).

I think I'll hold out for a DA42 though....;)

Cheers
EA

[IO540]

Another problem with a twin is that it is likely to be over 2000kg so you pay IFR charges. The DA42 isn't though, I think.

[bookworm]

A twin that will reach single engine control speed before rotation on a reasonable length runway, say 2200/2400 ft would be one way of making the selection.

Red herring I think, this rotation thing.

The issue is whether you can get to a speed at which you can safely fly away before you have to make the decision of whether to close the throttles or take the problem into the air. That requires consideration of the accelerate-stop distance at that critical speed.

Whether you make that decision on the ground or in the air doesn't makee much difference. Vmcg is often higher than Vmca.

[englishal]

The issue is whether you can get to a speed at which you can safely fly away before you have to make the decision of whether to close the throttles or take the problem into the air. That requires consideration of the accelerate-stop distance at that critical speed.
My philosophy on this is that if we're on the runway we stop regardless, if we're in the air and the gear is still down, then we land and stop regardless - if the gear is still down there is sufficient runway remaining. If we're airbourne and the gear is up, then we continue regardless. Whether or not continuing means we enter a slow descent and crash land is another matter, but the decision has been made.

Sometimes an aeroplane may be below Vmc during flight, for example just after a short field take off, which is very dangerous. If an engine failure occours then, the only course of action is to reduce throttle on the good engine and lower the nose, if you don't you're dead. This is when a ME aircraft is far more dangerous than a SE and is likely to catch out an unsuspecting pilot. Often Vortex kits are fitted, which may put Vmc below the stall speed so no chance of this happening.

Cheers
EA

[sunday driver]

Uninformed suggestion from a Sunday Driver - stay current (http://www.dft.gov.uk/stellent/groups/dft_avsafety/documents/page/dft_avsafety_500796.hcsp#P271_88101)
:(

[Timothy]

Sunday

I can't really see that the fact that this happened in a twin or single was particularly relevant. Both engines were working, it's just he didn' know how to work them. Sure, had he been more current on type they would probably have all survived, but that would have been true whether it had been a Baron or Bonanza IMHO.

Timothy

[cblinton@blueyonder.]

I agree with Timothy on this 100%

I was shot down in flames on another thread about flying IMC in a single over high terrain etc versus single flight over water.

The fact is in the cruise you are far safer in a twin!!!

What good is one of these fancy parachutes over water?
You still end up in the drink! just covered by a load of silk:confused:

[IO540]

I would expect the para would guarantee the plane ends up in the water in one piece; not guaranteed if ditching conventionally.

In the end the argument comes down to risk versus money, and if you really want to reduce risk then you can take an airliner.

[Phil Rigg]

Timothy et. al.,

Living in the Channel Islands (CI) really focuses the mind on the twin/single debate. Even in the best VMC when all good SE pilots are (arguably) at least as safe as ME pilots, the SE CI pilot (and his/her pax!) has to fly over miles of cold water with the prospect of a ditching and its unpredictable outcome followed by a maritime survival/recovery exercise in the event of engine failure.

Thus, there can be no debate, the answer has to be 'twin' even for flying only in brilliant sunshine, no wind, no cloud, no icing and infinite visibility! The two main questions facing the CI pilot are thus;

"How do I learn to fly in the shortest possible time to become competent enough to handle a "safe" twin hoping that I don't experience an engine failure before I get there?!!"

and

"Just exactly which aircraft is that "safe" twin?"

Remember that generally the "safer" the twin the more complex and the greater the training to learn both to fly it and to maintain currency. Interestingly, even if money was not an issue, the safer the a/c the more complex and thus the more training time needed to maintain currency to benefit from this safety. What the CI pilot is thus ultimately looking to optimise is safety vs the training time/useful flying time ratio overhead given the actual number of useful hours flown. This could become the a/c choice limiting factor over the money.

Simple eh?!!

After two years of mulling this around I have had many thoughts, including SE turboprop, converting a used BN Trislander(!) or even giving-up and paying Aurigny to fly me. I would be very interested to hear other instinctive comments regarding this unusual situation. I realise that training can be undertaken in "safer" geographical locations but the answer to which aircraft ultimately remains.

Thanks all, for your time,

Phil

[sunday driver]

Timothy & cblinton

Of course you're spot-on, and with far more experience than myself.

That particular incident occurred locally when I too was considering ME, and it made me consider carefully the safety trade-off between the undoubted benefits of duplicated systems, versus the draw-back of extra complexity. (The quoted bulletin implies that the unfortunate pilot was unable to solve a simple problem in a moderately complex aircraft in the time available, and also lost control).

In my case the decision was clear - I would not be getting enough hours to make me a safe ME pilot in that sort of aircraft.

I too would be interested in your opinions of a less complex twin - is there a need for a modern day Miles Gemini, or Aero 145?

Sunday

[Flyboy-F33]

Good post Phil,

What conclusions have you reached so far, regarding which safe twin?

I spoke to a guy who has use af A Baron 55, he also happens to be an airline pilot. He told me that on a recent trip to southern Spain, he flew the long way around (west coast) to avoid having to fly over the pyranees, stating that because the s/ec eiling was only 6000', the only place he was going was down (if one engine failed). A liitle over cautious I thought?

So that now brings in the question of turbo vs non turbo?

GG

[Timothy]

I don't think Phil is going to be bothered by a 6000' ceiling in the CI.

I am sure that I am going to be flamed, but I would say that among the less complex twins the ones that can be relied on to go up on one engine are:

Aztec
Baron
Late model Seneca (don't touch the early ones.)

Then going up scale a little
Navajo
C310
C4xx

I have opted for the Aztec because it has the performance and is cheap. It is also relatively simple. The complexity that kills is usually around the fuel management. C310 fuel management is pretty awful (OK when things are going OK, but a real trap for the unwary when you are perforce concentrating on other things). I can't remember about the Baron, but ISTR that it, too, is more complex than it needs to be.

Ironically, another problem for the low hour, low currency pilot is that some of these aircraft are too powerful. A 310, 421, B90 etc will have you over on your back and then pointing vertically down in a fly's fart if you don't catch the symptoms with rudder very quickly.

So, I say the Aztec (I would, wouldn't I, but it is why I chose it!), then the Seneca IV or V, finally either the Baron or Navajo.

Timothy

[Phil Rigg]

Flyboy,

The following new aircraft all potentially have the capability of offering true twin engine safety with minimal additional complexity but none of them are certified as yet let alone having 10 years of unblemished and field-proven service!

An example of existing engines on a new airframe is the Adam A500 centreline thrust twin with 2 x TSIOL540 350 hp turbo engines which has received some excellent flight test reports e.g."The asymmetrical thrust dragon is finally slain ...." etc. By all accounts if you loose an engine in the cruise you have plenty of time to figure out which one it is, shut it down, secure it and trim back to maintain altitude as you continue leisurely to your nearest diversion albeit at a slower cruise. Adam's adverts picture the a/c iin flight with the front prop stopped and feathered and the caption "Why make it harder than it needs to be?" Published SE climb is 400 ft/min on either engine at SL and MTOW.

An example of an old airframe with new engines is the Vulcanair P68C Diesel with 2 x SMA SR305 230 hp turbo diesel engines and fixed undercarriage. The original Partenavia P68C with 2 x IO360 200 hp falls into the category of "not going up on one engine" and only makes 130 kts in the cruise, however, the turbo diesels with matched props generate more thrust at a given hp to Avgas pistons and Vulcanair claim a 440 ft/min SE climb at SL and MTOW with a standard cruise of 160 kts. Add to this the improved reliability and many other claimed attractive features of turbo diesels over Avgas pistons through 70% less components etc. Also, SMA recently achieved JAA certification for running the SR305 at full 230 hp continuously which would be very important if one engine failed! Initially, certification at full power for 5 minutes only was granted with 200 hp for continuous operation.

An example of a new airframe and engines in a conventional twin configuration is the Diamond DA42 Twin Star for which a flight test report has been published in the April 2004 issue of a popular UK GA magazine.

Finally, a currently vapourware (i.e. prototype airframe and engines still under construction) example of a new airframe with engines mounted on rear fuselage pylons thus minimising the SE asymmetric thrust is the High Performance Aircraft TT62 using 2 x Thielert Centurion 4.0 310 hp turbo diesels.

Timothy,

Thanks for sticking your neck out and risking getting flamed. I very much appreciate your honest summary of the "best of the current bunch". I am in full agreement, endorse your comments completely and thus look forward to being flamed along with you!

Given their age, I am concerned about my ability to find an Aztec in airworthy condition you have owned yours long enough to get to know it. The same thoughts I hold true for the higher performance aging contenders that you mention e.g. Cessna 4xx potential wing spar ADs etc. along with concerns over increased handling complexity. The remaining immediate option is thus for a late model Baron or Seneca which, one assumes, have remained in production because of their better suitability to the low experience/low annual hours pilot over the rest of the bunch while I wait for the above developments to unfold.

Alternatively, I still fancy the used BN Trislander with a nice new executive interior and avionics refit would be pretty unique!

Hoping these comments have contributed in part to answering Flyboy's original question.

Best regards, respects and thanks to all,

Phil

[bluskis]

Phil

Check your PM

Bluskis

[Flyboy-F33]

Havn't heard of any of those types Phil.

I will probably go for a T310R unless the rumour I heard this morning is true....Avgas prices set to rise by 45%...!

All of a sudden a Mooney sounds quite appealing.

GG